Conventionally, a thermal-type airflow measuring device is employed to measure a flow rate of air by utilizing heat transfer from a heating element to air. The conventional thermal-type airflow measuring device is employed, for example, to measure a flow rate of intake air drawn into the internal combustion engine.
An airflow measuring device includes a case and a sensor. The case forms a passage of air. The sensor is located in the passage formed in the case. The case of the airflow measuring device is, for example, a resin hollow member having a hollow space. The case utilizes the hollow space as the passage of air.
For example, Patent Document 1 may disclose a method for manufacturing a resin hollow member. The method includes a primary forming step and a secondary forming step. The primary forming step includes to injection-mold resin to form a pair of half hollow members, such that each of the half hollow members has a half-hollow space. In the secondary forming step, the half hollow members are mated to form a resin filling space between the mated surfaces, and the resin filling space is charged with melting resin. Subsequently, the melting resin is solidified. That is, the half hollow members are joined together with secondary resin to manufacture the resin hollow member.
It is noted that, the manufacturing method of Patent Document 1 may have a concern that the joined portion between the half hollow members may have an insufficient strength. For example, in the resin hollow member formed by the method according to Patent Document 1, it may be difficult to enhance a joining strength between the half hollow members in a direction (mating direction) in which the half hollow members are opposed to each other.
Patent Document 2 may disclose to form a hole in a half hollow member to extended along a mated direction. Patent Document 2 may further disclose a secondary forming process to charge melting resin into the hole and to form a projected portion, which is greater than the hole in diameter, on the outside of the hole. It is noted that, the manufacturing method of Patent Document 2 includes to form the projected portion on the surface of the resin hollow member. Therefore, in a case where the resin hollow member is employed as, for example, a case of an airflow measuring device, the projected portion may cause turbulence in airflow around the surface of the airflow measuring device. Consequently, the turbulence may exert an adverse effect on measurement of airflow.